A direct (or sprue) gate is commonly used for single-cavity molds,
where the sprue feeds material directly into the cavity rapidly with
minimum pressure drop. The disadvantage of using this type of gate is
the gate mark left on the part surface after the runner (or sprue) is
trimmed off. Freeze-off is controlled by the part thickness rather than
determined the gate thickness. Typically, the part shrinkage near the
sprue gate will be low; shrinkage in the sprue gate will be high. This
results in high tensile stresses near the gate.

Dimensions
The starting sprue diameter is controlled by the machine nozzle. The
sprue diameter here must be about 1.0 mm larger than the nozzle exit
diameter. Standard sprue bushings have a taper of 2.4 degrees, opening
toward the part. Therefore, the sprue length will control the diameter
of the gate where it meets the part; the diameter should be at least 1.5
mm larger than or approximately twice the thickness of the part at that
point.

A smaller taper angle (a minimum of one degree) risks not releasing the sprue from the sprue bushing on ejection.